1. Field of the Invention
The present invention relates to optical energy reception apparatus and more particularly to a mechanism for searching a large field of view to detect a modulated signal source utilizing a detector apparatus having a smaller field of view capability by sequentially stopping and looking at sub-regions of the total field of view.
2. Prior Art
Initially, it must be recognized that detection of a modulation source in a field of view requires that the detector mechanism utilized must continuously look or stare at the region from which the modulated signal source is emanating since modulation necessarily infers that the signal to be detected is time dependent. Several techniques may be utilized to stare at a particular region in space having a defined field of view to allow detection of a source of modulated optical energy. For example, a detector may be incorporated which has a field of view capability equal to the field of view sought to be looked at. Such a device will always stare at the same region of space and is acceptable when the field of view in either the azimuth or elevation direction is of limited size. However, as the field of view to be looked at becomes larger, either the size of the detector apparatus itself becomes large and expensive or the detector apparatus will have a decreased detection effectiveness and capability. Consequently, when effective detection in a large field of view is desired several detectors having a more limited field of view capability may be utilized to look at contiguous field of view regions and thus cover the entire field of view. Again, such a technique is expensive because of the amount of detector apparatus required if a large field of view is to be interrogated.
The present invention utilizes one or more detection devices to obtain the required field of view in one dimension (e.g. azimuth) but utilizes the same detectors to intermittently and sequentially look at limited portions of the total field of view in the second dimension (e.g. elevation) until the entire field of view in that second dimension has been observed. The "stare" time for each portion of the field of view intermittently looked at is chosen to be sufficient to allow detection of a modulated signal source in that region. Thus, the present invention provides a reduced cost, compact apparatus to detect modulation signal sources in an enlarged field of view.